1. Field of the Invention
The present invention relates to a directional and stabilizing device for an aircraft with rotating wings having at least one rotor, which, in lift rotor configuration, is driven mechanically in rotation by at least one engine while absorbing the drive power at least partially, and such that the fuselage of the aircraft is subjected to the reaction of the drive torque driving the lift rotor, this reaction being compensated for by the device of the invention.
The aim of the present invention is more precisely to provide a directional and stabilizing device intended in particular for equipping helicopters having a single or main lift rotor, driven in rotation more particularly by one or several engines supported by the fuselage of the helicopter on which a torque is exerted due to the reaction of the drive torque of the lift rotor and which must be compensated for by an antagonistic torque of the same value.
In order to provide such an antagonistic torque, for a number of years the applicant has equipped his "Gazelle" and "Dauphin" type helicopters with a device known under the name of "Fenestron", and formed of a faired antitorque rotor. This latter includes a variable pitch multiblade propeller which, on the one hand, is mounted coaxially with a small radial clearance in a faired aperture of circular section formed transversally in the lower part of a vertical stabilizer integral with the rear end of a tail boom extending the fuselage of the helicopter rearwardly and, on the other hand, driven in rotation about the axis of the aperture, which is substantially perpendicular to the vertical plane of symmetry of the aircraft. The multiblade propeller is supported by an auxiliary gear box which is itself held in the aperture by rigid arms and which includes a set of bevel gears driving the propeller and itself receiving the drive movement from a transmission shaft which passes radially through the aperture and is connected to an output of the main gear box. The pitch of the blades of the propeller may be modified without action from the pilot by a servo-control also supported by the auxiliary gear box and actuated by a pitch control link which passes radially through the aperture and is connected by a linkage and/or cables to the rudder bar operated by the pilot of the helicopter. When the pilot gives a positive pitch to the blades of the propeller, the rotation of the propeller in the aperture, which is widened out in its inlet section, on one side of the vertical stabilizer, and which is slightly divergent as far as its outlet section, on the other side of the stabilizer, produces a transverse aerodynamic thrust which is exerted in the direction opposite the direction of air flow through the aperture, and this thrust develops on the fuselage, with respect to the axis of the main rotor, a moment opposing the drive torque of the main rotor, the transverse thrust developed by the faired rotor thus fills the antitorque function in stationary flight, whereas in forward translational flight, the antitorque rotor is gradually set by the pilot to a substantially zero pitch and the antitorque function is then fulfilled to a large extent by a lateral aerodynamic thrust which develops, proportionally to the square of the speed of movement, on the upper part of the vertical stabilizer, which is equipped with an aerodynamic profile having a camber and, possibly, a twist, and which is therefore shaped as a lift wing.
In stationary flight as in translational flight, yawing of the helicopter is controlled by a control variation of the thrust of the faired antitorque rotor, about its position corresponding to balancing of the drive torque.
With respect to the conventional arrangement of helicopter antitorque rotors, which includes a free rotor of a larger diameter than the faired rotor equipped with variable pitch blades and mounted for rotation in a substantially vertical plane about a transverse axis supported laterally by a pylon integral with a rear end of the tail boom, so as to generate, in all the stationary or translational flight configurations, a variable lateral force compensating for the reaction of the drive torque of the lift rotor and allowing the aircraft to be piloted when yawing, the advantages of the faired antitorque rotor are considerable, numerous and well known. Conventional tail rotors, especially on low tonnage helicopters, are very vulnerable to stones and gravel projected by the slip stream of the main rotor, close to the ground and on the ground, as well as with respect to bushes, branches and the ground itself, in the case of nose up landings, and they form a permanent danger for the ground staff. In flight, conventional rear rotors operate in a difficult environment and under poor aerodynamic conditions, and they are subjected to severe stresses and to dynamic phenomena which may be unstable, particularly at high forward translational movement speeds, since they are subjected not only to the relative wind but also to the slip stream and to the vortices caused by the main rotor, and the fuselage, and since there is interference between the antitorque rotor and the rear stabilizer of these helicopters reducing the efficiency of the assembly. In addition, the structure of conventional rear rotors is often complex and fragile, with flapping hinges subjected to high centrifugal forces coming from the blades and requires, for these different reasons, considerable maintenance and periodic replacement of numerous components of limited life or low potential between overhauls.
On the other hand, the faired antitorque rotor eliminates any risk of accidents for the staff and is itself protected from impacts with external obstacles, or with the ground during approaches and landings with the nose too far up. The faired rotor offers better aerodynamic efficiency and very substantially reduces the total aerodynamic drag of the aircraft at high speeds, whence a slightly lower consumed power in forward translational flight at high speed, and the possibility of reaching high speeds without excessively stressing the rotor components. In fact, at high translational speeds, since the pitch of the blades is practically zero, the blades and their control means only undergo very low alternate stresses, and the assembly of the antitorque rotor and the transmission which drives it only supports a low load, and should the faired antitorque rotor fail, the helicopter may come back to base in translational flight, without having to make an emergency autorotation landing, as is the case if the helicopter is equipped with a conventional antitorque rotor. Moreover, the low stress level in the blades in service and the elimination of the risk of instability of the rotor, because of the good flexional and torsional rigidity of the short blades of the faired rotor, mean that the lifespan of the blades is theoretically infinite. Furthermore, faired antitorque rotors, such as those fitted by the applicant to high light helicopters, require at the foot of each blade, neither flapping hinge, nor drag hinge, but only a pitch hinge which, considering the low radial loads to which it is subjected, and because the centrifugal axial loads of the blades are transmitted to the hub by a torsional member, it may be formed by a plane self lubricated bearing. The result is that the maintenance work on a faired antitorque rotor is considerably simplified.
It is well known that the aerodynamic efficiency of a faired rotor is greater than that of a conventional rotor with a free aperture of the same diameter, this feature is used for reducing the diameter of the faired antitorque rotor with respect to that which would be required for a free rotor, which allows it to be integrated in a vertical fairing of reasonable dimensions and, for equivalent efficiency, and, in stationary flight, to consume substantially no more power than a free aperture rotor.
In addition, although the combination in the same helicopter of a vertical stabilizer with lateral lift and a faired antitorque rotor, constructed in accordance with the French Pat. Nos. 1 593 008, 7820 258 and 83 04 448 of the applicant, advantageously fulfills and antitorque function and stabilization of the yawing helicopter, it on the other hand plays no active role in stabilizing the helicopter during pitching, particularly at high speed.
For this, it is necessary to add to the rear of the helicopter additional horizontal stabilizing surfaces, for example in the form respectively of two horizontal stabilizers, supported by the tail boom, on each side thereof, and just in front of the rear rotor. This results in a substantial increase of the structural mass.
2. Description of the Prior Art
To overcome these drawbacks, the French Pat. No. 2 167 249 of the applicant has already proposed fitting over the rigidified annular fairing, in which the faired antitorque rotor is housed, a "V" empennage called "butterfly" whose two branches extend above a horizontal plane passing through the top of the fairing housing the faired rotor, and each on one side of a vertical plane passing through this top, the two branches of the "V" empennage, having, on the one hand, mean planes extending symmetrically with respect to each other on each side of this vertical plane but having, on the other hand, aerodynamic lift profiles disposed antisymmetrically with respect to the general longitudinal axis of the helicopter. It has further been proposed that each branch of the "V" empennage has a substantially trapezoidal shape in a plane view and an aerodynamic profile such that an aerodynamic thrust is developed perpendicular to the plane of the empennage branch considered, this profile having a gradually evolutive configuration from the root, where it is symmetrical and thick, towards the end, where it becomes thin, either by remaining of the symmetrical type but with a linear twist about the longitudinal axis of the empennage branch, or by gradually becoming disymmetric with or without a twist about this longitudinal axis of the empennage branch, each of these branches being moreover, in the case of a rapid helicopter, equipped with a mobile trailing edge flap whose deflection is provided in the direction of the general twist of the profile and whose control is paired and coordinated, in a way known per se, with a longitudinal cyclic pitch control of the main rotor, of the helicopter, and only comes into action from a certain value of this longitudinal cyclic pitch. However, tests carried out on a directional and stabilizing device constructed in accordance with the teaching of the French Pat. No. 2 167 249 have not allowed all the advantageous results expected to be reached.
Furthermore, certain helicopter constructors equipping their aircraft with antitorque rotors of conventional structure have already slanted the plane of rotation of the rear rotors with respect to the vertical, which develops a force component in the vertical direction, this component having the drawback of being permanent (contrary to a faired antitorque rotor which produces no side thrust in cruising flight, for its blades then have a practically zero pitch). Some constructors have also mounted mobile control surfaces on the rear empennages of their helicopters, control of these mobile control surfaces being provided by automatically controlled actuators as a function of the manoeuvers in the air of the helicopter, by means of a processor receiving from numerous sensors information relative to a large number of flight parameters, which are taken into account for determining the angle of deflection of the control surfaces. The major drawback of these constructions is that they lack reliability, and require duplication of their electronic and electronic controls for ensuring the safety of the aircraft.